Day 3 - Advanced Linux Commands

Thus, Day 2 essentially addressed the fundamentals of Linux commands. We will now cover some advanced Linux commands that are necessary to write scripts.

Let's begin😎

1. chmod

    chmod(change mode) ->  To change the access mode of a file/dir.
    Ex :- chmod 777 test.txt
    Here 7 is "read + write + execute" permissions
    read = 4
    write = 2
    execute = 1
    And 3 times "7" means, we are giving all permissions to users, groups and others.
   

2. grep

    grep(global regular expression print) -> It searches a file for a particular pattern of characters, and displays all lines that contain that pattern.
    Ex: >cat test.txt
             Hi Smriti!!
             How are you?
             How was your day?
   
        >grep "How" test.txt
         o/p:-    How are you?
                  How was your day?
   

3. awk

    awk -> It filters the data in the form of column. 
    The awk command is a versatile text processing tool that allows you to manipulate and analyze text data. It can extract specific fields from a file, perform calculations, and format data.
    Default separator is "Space".
    Ex: >cat test.txt
             Hi Smriti!!
             How are you?
             How was your day?
   
        >awk '/How/' test.txt 
         o/p:-    How are you?
                  How was your day?
   
        >awk '/How/ {print $2}' test.txt   #Will print 2nd column
         o/p:-    are
                  was
   

4. find

    find -> Used to find files and directories and perform subsequent operations on them.
    Ex: find /home/Smriti *.txt
    Above command will give list of all files with ".txt" extensions present in the location /home/Smriti.
   

5. sed

    sed(stream editor) -> Used for manipulating text.
    It allows you to search for patterns in a text and perform various operations on the matching text, such as replacing it, deleting it, or printing it
    Ex: >cat fruits.txt
             Apple
             Mango
             Banana
             Mango
             Orange
   
        >sed 's/Mango/Kiwi/g' fruits.txt 
        #s -> substitution operator
        #Mango -> Search String
        #Kiwi -> Replacement String 
        #g -> global replacement
         o/p:- Apple
               Kiwi
               Banana
               Kiwi
               Orange
   

6. tail/head

    tail -20 filename -> To print the last 20 lines of a file
    head -20 filename -> To print the first 20 lines of a file
   

7. tar

    tar -> used to create Archive and extract the Archive files.
    Ex: tar xvf file.tar #Extracts files from an archive.
        tar cvf file.tar *.txt #creates a tar file which is the Archive of all .txt files.
   

8. top

    top -> displays all the running process within the environment of your system.
    It helps in monitoring system usage and performances.
    Ex: top -o %CPU #display a list of processes sorted by CPU usage.
   

9. ssh

    ssh(secured shell) -> used to securely log into a remote machine and execute commands on that machine.
    Syntax: ssh user@host
    where, user = username on the remote machine
           host = address or hostname of the remote machine.
    Ex: ssh user@192.168.43.120
   

10. scp

scp(secured copy) -> used to securely copy files between two machines.
Syntax: scp source_file user@destination_host:destination_path 
where, source_file = file to copy
       user = username on the remote machine
       destination_host = address or hostname of the remote machine
       destination_path = location on the remote machine where the file will be copied.
Ex:  scp file.txt user@192.168.43.120:/home/user/file.txt

*👆The information presented above is based on my interpretation. Suggestions are always welcome.*😊

~ Smriti Sharma✌